This invention relates generally to mechanical transmission apparatus and, more particularly, to gear-based transmission apparatus having little or no backlash effects.
Gear based transmission represents a very rigid and cost effective method for transmitting large forces at a very low cost when compared to cable and belt based transmissions. Gear based transmissions, however, must maintain clearance between the mating teeth of the gear sets that make up the gear train. This clearance, called backlash, exists in even the most precise of mechanisms to allow for misalignment, manufacturing variances, and material expansion and contraction due to temperature changes. In devices that are designed to transmit a torque or other forces in rapidly changing environments, such as force feed back mechanisms in simulator input devices, this backlash diminishes the response of the transmission system. For instance, when the input device needs to reverse the transmission of a force, the backlash causes a delay in the system response. This delay is particularly problematic for devices that use gear based transmissions to transmit torque and reverse direction rapidly while maintaining a high frequency response.
As the frequency of the system increases, the forces transmitted by the input device may decrease to such a degree that the time required to fully reverse the transmission exceeds the time needed to remove the clearance between the teeth, thereby resulting in no transmission of force at all. The problem of backlash limits the ability of the device to simulate effectively actual real world behavior, reducing its value in program simulation.
Embodiments of the present invention are directed to gear based transmission apparatus that are configured to reduce or eliminate the backlash effects. Controlling the backlash effects is particularly advantageous, for instance, for devices that use gear based transmissions to transmit torque and reverse direction rapidly while maintaining high frequency response. In specific embodiments, a dual motor, microprocessor controlled transmission is used to eliminate the backlash effects and improve the frequency response of the transmission. The dual motor transmission includes two motors with respective gears forming a double gear set. By controlling the motors individually to reverse out of phase with respect to one another, the backlash is systematically removed from one side of the gear set at a time. While the first motor maintains the force on the transmission, the second motor is removing the clearance between the gear teeth of the second gear set. Once the backlash is removed and the gear teeth of the second gear set are engaged to turn in the reverse direction, the second motor applies the required forces in the reverse direction, allowing the first motor to reverse and remove the backlash in the first gear set. The elimination of backlash by out-of-phase reversing transmission not only greatly improves frequency response, but it also reduces the noise caused by the gears during reversal.
In accordance with an aspect of the present invention, a transmission apparatus comprises a follower gear, a first drive gear set coupled with the follower gear to drive the follower gear, and a second drive gear set coupled with the follower gear to drive the follower gear. The first drive gear set includes at least one gear, and the second drive gear set includes at least one gear. A controller is coupled with the first drive gear set and the second drive gear set. The controller is configured to synchronize the first drive gear set and the second drive gear set to drive the follower gear in a first direction in a first transmission drive mode. The controller is configured to reverse the direction of the first drive gear set by a phase-shift time period before reversing the direction of the second drive gear set in a transmission reversal mode so as to reduce or eliminate backlash in the first drive gear set prior to engaging the first drive gear set with the follower gear to drive the follower gear in a second direction opposite from the first direction.
In some embodiments, the phase-shift time period is determined by the backlash in the first drive gear set and a speed of the follower gear. The phase-shift time period may be set to reverse the direction of the second drive gear set as soon as the backlash in the first drive gear set is at least substantially eliminated. The first drive gear set comprises a first motor pinion to be driven by a first motor, and a first drive gear coupled with the first motor pinion to be driven by the first motor pinion and having a first drive pinion connected therewith. The first drive pinion is coupled with the follower gear to drive the follower gear. The first drive gear set and the second drive gear set may be substantially symmetrically arranged with respect to the follower gear. The first drive gear set and the second gear set may be identical. The first drive gear set and the second gear set may have substantially the same amount of backlash. In specific embodiments, the controller is configured to synchronize the first drive gear set and the second drive gear set to drive the follower gear in the second direction in a second transmission drive mode after reversing the direction of the second drive gear set to reduce or eliminate backlash in the second drive gear set.
In accordance with another aspect of the present invention, a method of reducing or eliminating backlash effects in a gear transmission comprises providing a first drive gear set which includes at least one gear, providing a second drive gear set which includes at least one gear, and coupling the first drive gear set and the second drive gear set with a follower gear to individually drive the follower gear. The first drive gear set and the second drive gear set are controlled to synchronize the first drive gear set and the second drive gear set to drive the follower gear in a first direction in a first transmission drive mode. The direction of the first drive gear set is reversed by a phase-shift time period before reversing the direction of the second drive gear set in a transmission reversal mode so as to reduce or eliminate backlash in the first drive gear set prior to engaging the first drive gear set with the follower gear to drive the follower gear in a second direction opposite from the first direction.
In some embodiments, the method further comprises controlling the first drive gear set and the second drive gear set to synchronize the first drive gear set and the second drive ear set to drive the follower gear in the second direction in a second transmission drive mode after reversing the direction of the second drive gear set to reduce or eliminate backlash in the second drive gear set.
In accordance with another aspect of the present invention, a transmission apparatus comprises a follower gear, first drive means coupled with the follower gear to drive the follower gear, and second drive means coupled with the follower gear to drive the follower gear. A controller is coupled with the first drive means and the second drive means. The controller is configured to synchronize the first drive means and the second drive means to drive the follower gear in a first direction in a first transmission drive mode. The controller is configured to reverse the direction of the first drive means by a phase-shift time period before reversing the direction of the second drive means in a transmission reversal mode so as to reduce or eliminate backlash in the first drive means prior to engaging the first drive means with the follower gear to drive the follower gear in a second direction opposite from the first direction.